What would the 'first' of a species be, in an objective sense? As I understand it, speciation is a gradual process. Trying to pin down exactly where the change occurs is like trying to pin down precisely where a rainbow gradient shifts from green to yellow. You can pick a point and declare that to be the demarcation line, but discrete categorization in this way seems inherently arbitrary.

Even seeming straight forward metrics like "can they produce viable offspring" isn't so black and white, since between 'yes' and 'no' exists a continuum of 'maybe's. In very rare cases even horses and donkeys can have fertile offspring, e.g. mules that aren't mules (the typical infertility of mules has lead to the occasional use of the term to describe any infertile hybrid.)